MS Capacitor Replacement

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stipud
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MS Capacitor Replacement

Post by stipud »

So I finally had time this weekend to do the caps on my MPS2500. Special thanks to Cecil, Eric, Jim, Nico, Jason and all the others that help out with electronics repair on this forum. You guys made this possible!

All pictures here can be seen in high resolution on my pics site as well: http://photo.stipud.com/v/stereo/MPS2500/

So, here we are at the start of the game. Remove your bottom plate by removing 6 screws (in my case, all the screws were sheared off already :oops: ). This is what will greet you... those beautiful MS guts we all know and love! Engineering as art!
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Start by removing the endcaps (5 screws each), and all the connected parts. The speaker wires clip right off the board, and there are two screws that secure the shiny gold power rails (make sure you thread them back in so you don't lose them).
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I started pulling the powersupply capacitors in Jim Truett style:
http://phoenixphorum.com/viewtopic.php?f=6&t=8276

Unfortunately I wasn't so lucky getting them out. My caps took lots of force to remove (enough that I needed Wendy to hold the amp down while I pulled with both arms!), and a few of them broke off before they were removed. I am not sure I can recommend this technique based on the difficulties I had.

04/21/09 Edit: Eric D recently recommended rocking the capacitors back and forth gradually to get them out. Even if the leads break off, it's better than damaging the VIAs that connect the top and bottom of the board. You should avoid pulling them straight up like I did.

As you can see though, there's lots of electrolytic fluid under them.
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To get the transistors off, unscrew them slightly, and insert a pointy screwdriver under the top corner, then press in and it should pop right up. Be gentle with the little ones; they require far less force.
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Once you've got all the transistors lifted off the board, you can finish removing the screws. Make sure you keep them organized so you don't lose them, or forget which goes where. Take lots of pictures along the way as a reference!
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And here's what you end up with. To finish it off, there are 9 screws that connect the board to the heatsink. Remove them, and it will lift right out!
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Here's the side we're not so familiar with. As you can see, it rests nicely atop the torroids, so you don't have to worry about bending the transistors at all.
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And here's the naked heatsink. As you can see there's a sheet of plastic that lies between it and the board, to keep it from shorting out. You can also see that there's some crap under mine... It looks like this amp has had a bit of coffee spilled in it :oops:. Fortunately it's all dried up under the plastic side.
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Unfortunately I didn't have my camera for this step...

Start by removing the leftovers from the powersupply input caps. I did this with the amp hanging over the corner of my desk, pliers under the table (pulling down) and heating up the solder from the top, where you can see it and not make any mistakes.

The rail caps need to be removed the old fashioned way. Heat up one pad JUST until the solder gets fluid (then stop heating!), and pull the cap down on that side until it stops. Then do the same on the other side. Wiggle back and forth heating as little as possible (if you feel the amp getting too hot STOP or move to a different cap for a minute). Eventually you will hear them POP as they snap out of the circuit board.

After that, you should remove the solder from the holes. This will make installation much easier. Just use some solder sucker (braided copper) to pull the solder off of the board, leaving nice open holes to feed the caps through.

Once that's done, you can clean the amp. I used 99% isopropyl alcohol and a toothbrush. DO NOT USE 70% ISO... it will leave all kinds of crap residue. A neat trick is to get some air in a can. Once you've got the amp cleaned up, all you have to do is blow the iso off. I also let it dry overnight to make sure everything was dried out perfectly.

Which brings us here... there's a bit of discoloration around the PS caps, but the rest of the board cleaned up reasonably well. I could have gotten it cleaner but I am pretty lazy ;)
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I also cleaned all the coffee stains and thermal paste off of the heatsink and plastic sheet. For this, I just used some generic Lysol household cleaner, followed by isopropyl where the transistors mount to, to make sure there's nothing that will impede the conductance of heat.
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Here's a closer look at the rail cap section. You will see there are little rings where the caps wear on the board. This amp was probably mounted to a sub box.
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As you can see here, the rail caps I bought were a bit shorter than the factory parts. I could tell the top of my factory rail caps was scuffing on the underside of the bottom plate, so I erred on the small size.

I bought these: http://search.digikey.com/scripts/DkSea ... e=P6667-ND
But you could probably fit: http://search.digikey.com/scripts/DkSea ... e=P6669-ND

Since these rail caps are 35mm tall, moving to 35mm power supply input caps is also possible. I still prefer to stick to 105*C caps since it's not unlikely for the amp to get that hot.
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So now we're ready to take the amp apart. One last look...
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Here's an AWESOME trick I learned from Cecil that I highly recommend. Put a bead of RTV silicone down the trough in the middle of the powersupply capacitors. This will keep the two sides separated if the capacitor does start to leak, so it will make it less likely to short out. It also acts as a vibration dampener, AND it makes the caps super easy to install, since they stick in place.

Pull the leads through, and apply solder! Easy as pie! When you're happy with everything, and you've made a satisfactory bond between the amp and the board (make sure the solder forms a full bubble which adheres the wire), you can snip the leftover leads off.
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The rail caps are even easier, since they snap into the board. You just clip them in place, and apply solder. Hooray! Cap replacement is done!
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Now that you've finished, it's time to clean up the flux. Fortunately I got pictures of this part. Apply a bit of isopropyl to your toothbrush, and wipe it away. Finally, spray it with canned air, and it will disappear!
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Then you should be left with nice clean solder. I embarrassingly did a poor job of cleaning the old solder out, and I used generic stuff to replace it, so you can see it's not very shiny :oops:
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Now comes the hard part -- reassembly (really, this took me the most time!).

Cut up all of your sil-pads to fit the transistors nicely. The sil-pads I got from Nico were the perfect size for the big output BJTs, but they needed some cutting on all the smaller transistors. Make one good cut as a template, and then you can stack a few up and cut them together. It's better to err on the large side, rather than making something too small. Finally, test fit all of them. You shouldn't be able to see any exposed transistor.
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Once you've got your sil-pads ready, screw the board back in. You can start connecting the transistors now. Gently lower the sil pad underneath the transistor, and line the screw hole up. As you screw the transistor down, use a screwdriver or fingertip to keep the sil-pad from being twisted by the screw.
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Make sure all your transistors are sitting FLUUUUSH. If they are angled or not pressing down at all, then you risk blowing them up. If you find they are at an angle, don't panic! You can simply heat up the solder at their base, and press them down.
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Here's the finished product!
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Unfortunately all this fiddling around ended up breaking one of the RCA wires off. If you've gotten this far, it's a breeze to solder back together. I recommend that you learn from my mistake and tape it up before you have to do this, however!
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Now it's time to reassemble the amp. Screw the powersupply rails back in, connect the remote wire, and reinstall the endcaps.
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Finally, what we've all been waiting for.... I must admit my heart was racing at this point. You should probably be smart and install a small fuse before you do this, but what can I say, I was impatient :lol:. But.... IT WORKS! Make sure you test it in stereo and bridged, and fiddle with all your pots to ensure it's done.
Image

So there you go folks. Sorry I didn't get pictures of the actual soldering, but it's hard to hold a cap, solder, an iron AND a camera all at the same time :lol:
Last edited by stipud on Tue Apr 21, 2009 6:35 am, edited 3 times in total.
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Post by joerg »

Great job! Thanks for the pics! 8) They´ll help a lot when i do my SOFAS How long did it take u to replace the 16 caps? I´ll have to replace 84 of them! :shock: :shock: :shock:
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Post by stipud »

I probably spent 8 hours total, but I was slacking off heavily, and this was my first MS. Getting the amp apart took about 3 hours. I spent 2 hours cleaning it, and another 3 to reassemble. If you're not doing the rail caps you will save at least an hour.
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Post by dBincognito »

thedeal7235 wrote:i just noticed u used 10,000Uf- ive never gone any higher than 4700Uf-Interesting-
You should use a micrometer to measure the distance between the board and the heatsink and also the maximum width that you can work with

I actually go with much better caps.....wider and taller...higher temp. resistance, and increased capacitance

More Capacitance=Better SQ
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Post by joerg »

What are the digikey partnumbers for the MS275 caps and the MS2125 caps?
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Post by dBincognito »

If you have the brand, and the specs you can live chat with them and they will give you the part numbers....they are very helpful
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Post by Wakeup »

Nice screwdriver set...I have two sets of those very same ones myself...
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Post by stipud »

joerg wrote:What are the digikey partnumbers for the MS275 caps and the MS2125 caps?
Input caps are the same in all MS amps. The factory size is 18x31.5mm:
http://search.digikey.com/scripts/DkSea ... 93-1804-ND
http://search.digikey.com/scripts/DkSea ... =P11210-ND

You can go up to 35mm height as well, to match the rail caps, but it is a tight fit. I've found this one from United Chemicon (another good capacitor brand), which is still 105*C rated, and has 8200uF vs the 5600uF in the smaller ones:
http://search.digikey.com/scripts/DkSea ... 65-1949-ND

I went with the Panasonics because they have a higher rated life on paper than the Nichicons (5000 vs 1000 hours at 105*C), and because they are well regarded for power supply purposes. Most of us use the Nichicons with good results as well, and they are very highly regarded by most audiophiles. Considering how many caps you have to replace, I would probably recommend the Nichicons, since they are half the price of the Panasonics, and should still last another 15 years.

Rail caps are different, depending on the amp. I think the MS275 has 35v rails just like the MPS2500, but the MS2125 is 50v? You'll have to check yours to be sure. They are all 35x35mm, so just fill it in the capacitor search here:
http://search.digikey.com/scripts/DkSea ... Cat=131081

You can ctrl-click to select multiple fields, so I would search for:
Maximum Temperature: ctrl-click on all the 105*C + rated fields
Size / Dimension: pick the size you need
Voltage Rating: voltage of your cap

It's that easy 8)
Last edited by stipud on Mon Mar 16, 2009 2:04 pm, edited 1 time in total.
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Post by nico boom »

GREAT WORK TOM! 8)
It took you about 8 hours; good job :shock:
I have worked on some amps for around 18 hours to get them 100% again. [somebody worked on those already, and I had to tidy up the mess while replacing the caps....
So I guess I'm out of bussiness now; everybody knows how-to-replace-caps. [it's only when the amp does not work afterwards that things get interesting :wink: ]
You did a great job, now put a sinewave signal into it, connect your scope and DMM, and check how that goes; I do that before listening to music with the amp. :D
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Post by thedeal7235 »

NICE JOB, ive also used the united chem for rail caps, they work great-(ur right its veryhard to solder, take pic, etc.- :D :D
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Post by neverman »

So where are those screwdriver sets sold? Happy with them or is there a step-up from those?

Nice job on the caps. Little sad you didn't get better solder, small price to pay for "shiny-shiny" :)
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Post by Wakeup »

I usually get them from Harbor Freight. They are throw away sets....to me...I have like 3 or 4 sets....
And then I have my wiha set.

But for the $7~ cost....I dont get mad if I lose a bit or damage one here and there.
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Post by bogart »

Man, that is pretty cool, great job. I intend to do my outlaw myself and you guys and this forum is the only reason that I think I can swing it. Great job and thanks for all the pics
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capacitor brands help

Post by KUB3 »

Hi guys, I replaced loads of PG caps a couple of years ago in both M and MS amps. I think I used Panasonic from memory. However I will have quite a few more MS amps to do shortly.

So what do you think are the best make of caps out there? I have seen Black Gate but they seem rather expensive. ANy other brands to look out for?

Also, does it matter if the capacitance is nt exactly the same as the originals?

Thanks...
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Re: capacitor brands help

Post by stipud »

KUB3 wrote:Hi guys, I replaced loads of PG caps a couple of years ago in both M and MS amps. I think I used Panasonic from memory. However I will have quite a few more MS amps to do shortly.

So what do you think are the best make of caps out there? I have seen Black Gate but they seem rather expensive. ANy other brands to look out for?

Also, does it matter if the capacitance is nt exactly the same as the originals?

Thanks...
Considering these capacitors are just to stabilize the input and rail voltage, and are not directly in the audio signal path, I don't think the "sound quality" of the capacitor is worth worrying about. Instead I would look for whatever cap offers the most capacitance, the strictest tolerance, and the longest rated life at 105*C.

There may still be minute sonic changes that may occur from the way the input or rail voltage is stabilized, but they are negligible compared to other external modifications, like sound deadening and proper installation. Hypothetically if you were to upgrade caps for sound quality, I would think that the rail capacitors have the greatest possible sonic impact (since they power the output of your amp), while you should instead focus on maximizing the capacitance of the power supply 12v caps. Or better yet add a big 12v 1 farad cap, which does exactly the same thing, only better (reject A/C ripple on your D/C power feed).

Even better, if you get a capacitance meter, you can measure the actual capacitance of your caps, so that you can match the capacitance of each bank, so that both of your channels have as little difference as possible. The less capacitative difference between the channels, the more similar your channels will sound. Of course you would probably need to buy a lot of extra capacitors to make it worthwhile, but considering you are doing several amplifiers, that may work out perfectly for you.

Let's not forget that your old capacitors have likely lost some of their capacitance over the years. As technology has improved, we have also managed to pack more capacitance into the same footprint as before. So just putting in new caps, regardless of brand, usually gives a large SQ boost.
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Post by brenzbmr@sb »

just to add to what tom said about any cap is an improvment over the tired ones inthere

i did one of my 2125s both input caps with (8800uf) and i got some 50v(10,000uf) for the rails.

its a very noticeable difference between the one i did and the one i didnt do. so ifu have time and some xtra cash i would recommend u do it.
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Post by KUB3 »

What are your views on using sil paste? Is this required? Or can you just use sil pads alone? My original amps have pads and paste. I have both to hand, so please describe the ideal method...
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Post by KUB3 »

I've just stripped three more amps. I found slowly wiggling then bending the small caps from one side to the other worked well. Then just snipping their leg wires was very easy. I did not use any force at all. Just gentle bending. All went perfectly.

The large caps were trickier. I also went with your method: heat up the leg solder then quickly move a fraction to the side. Then repeated a dozen times for each leg until the cap was free. All but one leg went perfectly...

On one a small metal disc had removed. But I can see it has no electrical benefit, as it's on the side of the board that goes no where. The solder pad on the other side is still there. This may have some minor structural effect, but nothing to worry about I hope... (discuss)...?

As it should be...
Image

Tag missing on one side only... (luckily the side that goes nowhere)
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Post by KUB3 »

ps

(where has the edit function disappeared too?!)

On these revision "I" models of the MS275 (the newer ones) there were no leaking caps at all. This is the first time I've done this to discover all was ok after all. Better to be safe though :)
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Post by Eric D »

I don't use paste with sil-pads. The pads are designed to make full contact on their own with sufficient pressure. Besides, paste can be messy (I have had it all over me and amps I have worked on before). Pads alone may not conduct heat as well as pads with paste, but the MS amps which use pads are not all that demanding on the parts anyway. If you look at the MS2250 though, things are different. This amp uses no pads and has the devices mounded directly to the heatsink with paste, for the best possible heat transfer. The whole heatsink is anodized to keep the parts isolated.

The pad you removed on your MS275 is not a big deal. However the via next to it is. That looks damaged to me. If you don't make 100% certain the top and bottom are electrically connected when you solder the cap in, your amp will likely fry when you turn it on. When I replace these caps I make note of an area near the cap I can probe with my DMM once the cap is in place and I check conductivity from the bottom of the cap to the board top side. In your photo you can probe the screw to the bottom of the cap.

Also for anyone else reading, if your rail caps (the big ones) don't look physically bad, don't replace them. I have yet to find one leaking. The smaller 2,200uF caps are the problem. I have seen many thermally damaged rail caps though, and in this case it looks better if you replace them.
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Post by KUB3 »

Thank you Eric. I have not yet removed every spec of solder from inside the holes yet. So I think that is a bit of solder rather than damage :) I had started using some copper solder wick, rolled up and pushed inside the holes, then heated up to remove the solder. But this takes me a while and I've only done a couple. It's getting dark here now so work will resume tomorrow in the daylight.

Anyone know what date the "I" revision was? It's clearly not old enough to have needed caps yet. So this may provide a guide to some others. All the other amps I had before were older and every one had (hidden) leaking caps.
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Post by Eric D »

Heat makes caps fail quicker. Since your MS amps are in excellent condition, they were likely well taken care of. When I did the caps on my MS275 "REV I", they were leaking. But my amp had rust and dents in the sink, so I would not doubt the owner beat on the amp and had it very hot many times.

I have also replaced caps on very old MS amps and found them not to be leaking (most are not this way). Heat has a lot to do with it.
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Post by marko »

the caps in my very early mps2500 (both rca's together) are differant from later caps and i'm sure they are original, they look like brand new still with no signs of leaking! i think pg screwed up with choice of cap supplier tbh. all my hifonics amps still run on the original caps and i've never seen one leak yet.. there are almost 20 years old!

it's very easy to lift those vias, lower heat is needed or a regulated soldering iron.
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Post by KUB3 »

I went through four different irons today! The first was far too under powered and nowhere near not hot enough. Then I got my portable gas one out, which took ages to heat up but then it still didn't seem hot enough. Then I pulled out the really big gun, which ran so hot it died before I could even use it. Finally I found my very last one and it was just right. Goldilocks and the soldering irons :lol:
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Post by nico boom »

I trust you have red all the info that Eric, Tom, Jim, and others including myself have posted about this subject Paul.... :wink:
Essential is , like Eric stated, to check the via's for contact through the board!
I always replace the railcaps as well, while having the board in my hands; it's just my preference, but indeed, never seen a leaking one [since I only have mint [not abused] amps, that seems logical].
When in doubt of a via, be sure to use Eric's [drill a hole next to the old one ] method, or mine, using solder wick through the existing hole.
Good luck Paul, and treat them well!
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